Drill countersinks are known in the art for receiving and holding a drill bit. An example prior art countersink is illustrated in FIG. 9. The countersink tool 10 includes a proximal end 12 with a shank 14 and a distal end 16 with a cutting edge 18. The shank 14 includes an annular groove 20 for connection with an automatic or “quick-release” coupling of a drill chuck to a holder (not shown). The shank 14 is of any suitable shape for rotatably engagement with a power source, using either a male or female coupling.
The countersink tool 10 includes a longitudinal bore 22 extending from the cutting edge 18. The bore 22 is adapted to receive a drill bit 24 therein having a diameter corresponding to that of the bore. The countersink tool 10 includes a body 27 having an outer wall 28 with a flute 26 formed at the distal end 16, which includes the cutting edge 18. The drill bit is held in place within the bore 22 by a set screw 30 which extends through the body 27 to engage the drill bit 24. Loosening the set screw 30, releases the drill bit 24 to adjust the length of the bit 24 extending from the distal end of the bore 22, and tightening the set screw 30 secures the drill bit within the bore 22 relative to body 27.
The illustrated countersink tool 10 is a single stage countersink with a single flute. Two stage countersinks are also known in the art for forming a counterbore having two diameters. Countersinks with more than one flute and/or set screws are also known in the art. Also illustrated is an adjustable stop collar 42 or depth stop attached to body 27 of the countersink tool 10. The depth stop 42 is placed upon the fluted portion of the countersink 10 to prevent an operator from drilling a counter bore too deep with the countersink tool 10. The conventional depth stop 42 is a simple ring having an inner diameter corresponding to the outer diameter of body 28. The depth stop collar 42 includes a workpiece engagement surface 43 and a set screw 44 to secure the collar in place along the length of the body 27 of the countersink tool 10. Loosening the set screw 44 releases the stop collar 42 to permit an operator to adjust its position along the length of the countersink tool 10 and tightening the set screw 44 secures the collar in place relative to the body 27. Thus, the depth of counter bore is adjustable in two ways, by adjusting the length of the drill bit extending from the bore 22 with the countersink set screw 30, and by adjusting the position of the stop collar 42 along the length of the countersink tool 10 with the depth stop collar set screw 44, thus fixing a counter bore depth D between the work engagement surface 43 of the stop collar 42 and the cutting edge 18 of the body 27 of the countersink tool 10.